Alopecia Areata, patchy hair loss which may progress to total scalp or body hair loss, affects 1-2 percent of the population. We hypothesize that Alopecia Areata is an HLA (histocompatibility locus antigens) restricted, T cell mediated autoimmune reaction to hair follicle antigens or viral infection resulting from the interactions of multiple genes of immune response which may result in the production of specific antibodies to the hair follicle. Alopecia Areata occurs with other autoimmune diseases, in identical twins and in families. It is associated with HLA alleles and with other immune related genes that may interact to determine susceptibility, resistance, and persistence. Possible viral infection and antibodies to hair follicle, melanocytes, keratinocytes, and endothelial cells are of unknown significance. Our goal is to investigate the genetic mechanism of Alopecia Areata in families of the purpose of disease prevention, early intervention, and development of specific therapies. We propose: a) to identify and collect DNA from AA families; b) to determine the genetic models for Alopecia Areata by using the simultaneous information on both the aggregation and association of the HLA marker with the disease and also on the risk of being affected for some relatives of a patient; c) to identify disease-predisposing amino acids in the HLA region involved in the Alopecia Areata process; d) to identify polymorphic markers for genetic loci that are associated with Alopecia Areata in families. To accomplish aim a we will collect families from several dermatology clinics in Houston. For aims b and c we will apply MASC and haplotype methods. For aim d, we will use parametric and nonparametric linkage methods.